Baseline Widely available
Note: This feature is available in Web Workers.
The observe()
method of the PerformanceObserver
interface is used to specify the set of performance entry types to observe.
See PerformanceEntry.entryType
for a list of entry types and PerformanceObserver.supportedEntryTypes
for a list of entry types the user agent supports.
When a matching performance entry is recorded, the performance observer's callback functionâset when creating the PerformanceObserver
âis invoked.
options
An object with the following possible members:
buffered
A boolean flag to indicate whether buffered entries should be queued into the observer's buffer. Must be used only with the type
option.
durationThreshold
A DOMHighResTimeStamp
defining the threshold for PerformanceEventTiming
entries. Defaults to 104ms and is rounded to the nearest of 8ms. Lowest possible threshold is 16ms. May not be used together with the entryTypes
option.
entryTypes
An array of strings, each specifying one performance entry type to observe. May not be used together with the type
, buffered
, or durationThreshold
options.
See PerformanceEntry.entryType
for a list of valid performance entry type names. Unrecognized types are ignored, though the browser may output a warning message to the console to help developers debug their code. If no valid types are found, observe()
has no effect.
type
A single string specifying exactly one performance entry type to observe. May not be used together with the entryTypes
option.
None (undefined
).
This example creates a PerformanceObserver
and watches for "mark"
and "measure"
entry types as specified by the entryTypes
option given in the observe()
method.
const observer = new PerformanceObserver((list, obj) => {
list.getEntries().forEach((entry) => {
// Process "mark" and "measure" events
});
});
observer.observe({ entryTypes: ["mark", "measure"] });
Watching a single performance entry type
The following example retrieves buffered events and subscribes to newer events for resource timing events (PerformanceResourceTiming
) using the buffered
and type
configuration options. Whenever you need to configure the observer to use the buffered
or durationThreshold
option, use type
instead of entryType
. Collecting multiple types of performance entry types will not work otherwise.
const observer = new PerformanceObserver((list, obj) => {
list.getEntries().forEach((entry) => {
// Process "resource" events
});
});
observer.observe({ type: "resource", buffered: true });
Specifications Browser compatibility
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HTML:
3.2
| Encoding:
UTF-8
| Version:
0.7.4